On the road bike I am trying to fix, I ran into another problem. The seat post is stuck inside the tube and I have tried lubing and it and letting it set, taken pliers to it, even lightly tapped the seat post with a hammer to see if I could jar it loose. It was in a shed for several winters (in the rainy NW) and it probably has some rust in it, but it will simply not budge. Any thoughts of how to get it out? It is an old steel post and I can easily find a used alloy one at the shops here so there is no need to keep it in good working order. Thanks.

Depending on the severity of the corroded and chemically welded parts there is one "trick of the trade" fitters would use to free heavily corroded bolts. Heat. If you have access to a soldering torch, not electric but flame, you cold heat the seat tube whilst applying a twisting pressure too the seat post. If this doesn't work then the corrosion may be so bad that too much of the metals have corroded and a new seat post will be too sloppy anyway.
Worth a try.
If that doesn't work, cut the seat post about an inch above the seat tube and try a hacksaw blade cutting the inside of the seat post. Cut as deep as you can along the length inside and then grip with large multi grips and try and twist it free.
Regards,
Rick.

I have a 30 year old bike and the alloy seat post has probably been sitting in the seat tube for the last 30 years. It seems the bike has been stored indoors throughout its life so the situation shouldn't be that bad, but I just couldn't move it! Sprayed WD40 from the top and tried to twist and pull it with the saddle and no luck. Sheldon Brown's site suggests soaking it with ammonia, but it requires taking out the BB and administering harmful chemicals into the frame, which I am really reluctant to do unless I have no choice.

I paid a visit to the LBSs. The first one, without even trying, said they have to charge $100 minimum. Obviously they didn't even want to take the job. The second one got it out for me in 10 minutes, for free!

The LBS owner first tried twisting with the saddle; then tried twisting with a vice grip; neither worked. He then sprayed some degreaser on the top, add a few drops of wet lube, and started hammering down on the seatpost. This seemed to be the magical move that "broke the seal" as the seatpost did get hammered down the tube after a few blows. As soon as it moved, it was easily twisted and pulled out with the vice grip. Frame saved, seatpost saved, saddle saved, BB untouched, no chemical down the frame. Didn't see much aluminum oxide on the seatpost. It was mostly rust from the steel frame.

So hammering down on the seat post is an effective way to break the seal, provided your seat post has a solid capped end (mine does) for the hammering to take place without harm.

As an aside, the LBS owner said he's never seen a seat post like mine: a solid top and such short length.

Patience, patience, and more patience, that is the trick to freeing the seat post. My project is a 20 yr. old Burley tandem and both seat post were frozen in place. P.B. didn't touch the corrosion on the aluminum seat post but did work once the seal was broken that had formed between the post and the chromoly frame. For that is took applying ammonia every day for 1 week straight and then removing the seat and flipping the bike over and placing th post in my bench vise and using the frame as leverage. This was not as easy as it sounds. 1st I pulled my bench out of the wall, then once I re-attached it and double the screw size holding it to the wall and re-enforcing the bolts holding the vice to the bench, I proceeded to actually break the vice. Yes, I said I broke the vice. Once that seal was broken the P.B. was able to seep in and help get rid of the rust and I was able to coax the post out with a pipe wrench. I'll be replacing at least one of the post if not both and giving the inside of the seat tube a thorough cleaning before I install new ones. Also I'll be sure to remember the no.1 rule of installing a seat post.....lubrication.

i have a similar problem but might be more complicated... i have a devinci taos and have had a carbon seatpost for 3 years... but now the post is stuck... tried lube.. heat is out of the question due to the plastics covering the carbon... any ideas to save the seat post and not hurt my baby.

Hmm Never heard the ammonia trick. Interesting. Some of the best penetrants according to tests in ascending order: Liquid wrench, Kroil and best home made brew of acetone and ATF(automatic transmission fluid) fluid 50/50 mix. Let soak over night and rap it a few times as you add penetrant. Than using a piece of wood like a 2X4 put it on the seat post to protect it and hit it with hammer.

You can use heat but NOT flame around penetrants, a heat gun or a hair dryer , and hit it again and add penetrant..

No Idea about carbon frames, did not think that could happen. Would not use acetone, liquid wrench might be OK. Contact bike maker for compatible products.

Do the research to make sure whatever you use is not going to damage the CF. Try to find out what kind of corrosion is common for Carbon Fiber and what can be safely used to dissolve it. Like I said in my original post, "be patient". Especially since you are dealing with a much more expensive material that I was.

Hello, I'm a first-time poster and I'm bumping an old thread to the top here, but this one seems particularly relevant to my case.
I noticed my seat post was stuck a few weeks ago. It's a chromoly road frame; I don't remember the seatpost make off the top of my head, but a knowledgeable guy I trust at a LBS told me that it was aluminum, and mentioned that the aluminum oxidizing can cause the post to seize and that acids (ammonia and Coke were the two he told me of) work better than oil to unstick the post.

So. I started out dribbling windex (weaker ammonia solution before going to the strong stuff) into the crack between the post and the tube.
Then I tried putting strong ammonia (as sold at drugstore) into the crack.
Of course I wiggled, tapped with a hammer and tried to twist between these applications.

Then I took the cranks off and the BB out, tried to close the aforementioned crack with silly putty, and pour ammonia into the seat tube from the bottom. The silly putty didn't seal up the crack at all once it got wet, so the ammonia leaked out. Thought of trying something else (clay? rubber cement? the sticky stuff that people hang posters with?) but not sure what else would be more liquid-resistant.

Then I bought a sink stopper to stop up the bottom of the seat tube and tried to pour ammonia into the post-tube gap, but it became clear that too much of it would dribble out where the binder bolt went, the stopper didn't fully seal, and it was a horribly inefficient, if not impossible, way to get ammonia into the tube.

Those who said ammonia worked for you - how did you get it in there? Did you try to fill the seat tube with ammonia or was it enough to just have it trickle down past the stuck parts?

I'm about to give up on the chemical method just 'cause it doesn't seem like there's any effective way to apply the chemical but I would be glad to be wrong about it.